1. Field of the Disclosure
The disclosure relates to improving the performance of patient monitors through low noise cabling.
2. Description of the Related Art
Oximetry utilizes a noninvasive optical sensor to measure physiological parameters of a patient. In general, the sensor has light emitting diodes (LEDs) that transmit optical radiation into a tissue site and a detector that responds to the intensity of the optical radiation after absorption (e.g., by transmission or transreflectance) by, for example, pulsatile arterial blood flowing within the tissue site. Based on this response, a processor determines measurements for oxygen saturation (SpO2), pulse rate, plethysmograph waveforms, perfusion quality index (e.g., an index that quantifies perfusion), assessments of other blood constituents, parameters or analytes, including for example, a percent value for arterial carbon monoxide saturation (HbCO), a percent value for methemoglobin saturation (a brownish-red form of hemoglobin that cannot function as an oxygen carrier) (HbMet), total hemoglobin (HbT), fractional SpO2 (SpaO2) or the like. Additionally, caregivers often desire knowledge of HbO2, Hb, blood glucose (HbGu), water, the presence or absence of therapeutic drugs (aspirin, Dapson, nitrates, or the like) or abusive/recreational drugs (methamphetamine, alcohol, steroids, or the like), concentrations of carbon dioxide (CO2), oxygen (O2), oxygen concentration, pH levels, bilirubin, perfusion quality, albumin, cyanmethemoglobin, and sulfhemoglobin (HbSulf), signal quality or the like. It is noted that “oximetry” as used herein encompasses its broad ordinary meaning known to one of skill in the art, which includes at least those noninvasive procedures for measuring parameters of circulating blood through spectroscopy. Moreover, “plethysmograph” as used herein (commonly referred to as “photoplethysmograph”), encompasses its broad ordinary meaning known to one of skill in the art, which includes at least data representative of a change in the absorption of particular wavelengths of light as a function of the changes in body tissue resulting from pulsing blood.
Oximeters capable of reading many of the foregoing parameters during motion induced noise are available from Masimo Corporation (Masimo) of Irvine, Calif. Moreover, portable and other oximeters are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952, and 5,769,785, incorporated by reference herein, and others patent publications such as those listed at http://www.masimo.com/patents.htm. Such reading through motion oximeters have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios.
The detectors of the noninvasive sensors read by many of the foregoing patient monitors generate one or more low-level signals that are susceptible to corruption from various noise, such as electromagnetic interference (EMI) and internal noise that originate in the sensor, cabling and monitors. One internal noise source is due to a triboelectric effect, which includes static charges that build when two materials rub together. For example, when a cable housing detector wires is flexed, impacted, or the like, the detector wires may rub together and triboelectric noise can be induced in the detector signal. These induced triboelectric noise spikes can be orders of magnitude larger than the desired low level detector signals.
To alleviate the buildup of triboelectric charges, low noise cable manufacturers included graphite coatings exterior to, for example, the cabling configured to communicate detector signals. However, the graphite gel used in the manufacturing process proved difficult to apply and remove. Because of these and other difficulties, manufacturers began substituting the graphite coatings with a coextruded conductive PVC sheath around, for example, their sensitive signal carrying cables.